The aim of this project is to establish the role of the rheological properties of blood cells in circulatory regulation in health and disease. The blood cell properties to be studied are the deformability of red blood cells (RBCs) and white blood cells (WBCs), RBC aggregation, WBC adhesion to vascular endothelium, and the concentration of RBCs and WBCs. Homologous blood cells with alteration in the above-mentioned properties will be administered either by isovolumetric exchange transfusion into the entire circulation or by perfusion into individual organs. The resulting changes in hemodynamic functions, oxygen transport and vascular permeability will be determined in vivo and correlated with the alterations in rheological properties of blood cells assessed by in vitro experiments and theoretical analysis. The results will be correlated with the changes in the molecular organization of membrane and the flow dynamics in microcirculation. The multidisciplinary approach is used to study the role of blood cell properties (RBC deformability, RBC aggregation, WBC deformability and WBC adhesion) on circulatory dynamics in terms of regional blood flow and oxygen delivery. The changes in blood flow and resistance will be analyzed by taking into account the neurohumoral factors which may affect the vascular hindrance, in addition to blood rheology. The ultimate aim is to elucidate the role of blood cell rheology in some of the pathophysiological mechanisms of hematological and circulatory diseases.